Leap Year Checker

What Is a Leap Year?

A leap year is a calendar year that contains an extra day — February 29 — making it 366 days instead of the usual 365. Leap years exist to keep our calendar synchronized with Earth's revolution around the sun, which takes approximately 365.2422 days. Without the extra day every four years, our calendar would drift by about 24 days every century, causing seasons to gradually shift out of alignment with the months we associate them with.

The rule for determining a leap year is: a year is a leap year if it is divisible by 4, except for century years (divisible by 100), which must also be divisible by 400. So 2000 was a leap year (divisible by 400), but 1900 was not (divisible by 100 but not 400). The next leap year after 2024 is 2028.

The Leap Year Rule Explained

The Gregorian calendar uses a three-part rule to determine whether a year gains an extra day:

• Divisible by 4: The year must be evenly divisible by 4. For example, 2024, 2028, and 2032 are all divisible by 4 and are therefore leap year candidates.
• Century exception: If the year is also divisible by 100 (a century year), it is NOT a leap year — unless it also passes the next rule. So 1700, 1800, and 1900 were not leap years despite being divisible by 4.
• 400-year override: If the year is divisible by 400, it IS a leap year regardless of the century exception. The year 2000 is the most recent example — divisible by 400, therefore a leap year. The next will be 2400.

In code, this logic is often written as: (year % 4 === 0 && year % 100 !== 0) || year % 400 === 0. Our checker applies exactly this rule for complete accuracy.

How to Use the Leap Year Checker

1. Type any year into the Year field (e.g., 1900, 2000, 2028).
2. Click Calculate.
3. The result immediately tells you whether the year is a leap year or not.

Key Facts About Leap Years

• Leap years occur roughly every 4 years — but not always (century exception applies)
• The Gregorian calendar has been the international standard since October 1582
• There are 97 leap years in every 400-year cycle under the Gregorian system
• People born on February 29 are sometimes called "leaplings" or "leap-day babies"
• February 29 has legal significance in some countries — contracts and age calculations may treat it specially

Frequently Asked Questions

• Why do we need leap years?
  Earth takes approximately 365.2422 days to orbit the sun, not exactly 365. Without a correction, our calendar would drift by about one day every four years — roughly 24 days per century. Leap years add an extra day periodically to keep the calendar aligned with the astronomical seasons.
• What is the leap year rule?
  A year is a leap year if: (1) it is divisible by 4, AND (2) it is not a century year (divisible by 100), unless (3) it is also divisible by 400. In practice: 2024 is a leap year (divisible by 4, not a century year). 1900 was not (century year, not divisible by 400). 2000 was (divisible by 400).
• Was year 2000 a leap year?
  Yes, 2000 was a leap year. Although it is a century year (divisible by 100), it is also divisible by 400, which means it qualifies as a leap year under the Gregorian calendar rules. This confused many early computer systems that only applied the "divisible by 4" rule.
• How many days are in a leap year?
  A leap year has 366 days. The extra day is added to February, giving it 29 days instead of the usual 28. All other months retain their normal lengths. The next leap year after 2024 is 2028.